In general, there are through-away chips, drills, solid-type end mills, and the like, as coated tools. Through-away chips are used by being attached detachably to the front end portion of a bite in lathe turning machining and planning machining of a work made of various steels, cast ions, or the like. Drills are used in drilling cutting machining or the like of the work. The solid-type end mills are used in facing cutting machining, grooving machining, shoulder machining, or the like of the work. In addition, thorough-way end mill tools, which are used by being attached detachably as in the above-mentioned through-away chips in cutting machining as in the above-mentioned solid-type end mills, are known.
For example, a coated tool, in which a hard coating layer made of a complex nitride layer of Al and Cr (indicated by (Al, Cr)N hereinafter) is vapor deposited on the body (referred as cutting tool body herein after) made of tungsten carbide (referred as WC herein after)-based cemented carbide, is known as a coated tool as indicated in Patent Literature 1 (PTL 1). The conventional coated tool shows excellent cutting performance since the above-described (Al, Cr)N layer constituting the hard coating layer has excellent high-temperature hardness, heat resistance, high-temperature strength, high-temperature oxidization resistance, and the like.
Also, it is known that the conventional coated cool can be manufactured by following procedure described below. First, the cutting tool body is inserted in an arc ion plating apparatus which is one of physical vapor deposition apparatuses as shown in FIGS. 1A and 1B. Second, arc discharge is generated in the condition in which electric current is 90 A between the anode electrode and the cathode electrode on which Al—Cr alloy with a predetermined composition is set in a condition in a state where the cutting tool body is heated to 500° C. by a heater. Simultaneously, nitrogen gas is introduced in the apparatus as reaction gas to obtain reaction atmosphere of 2 Pa. In regard to the cutting tool body, the above-described (Al, Cr)N layer is vapor deposited on the surface of the cutting tool body in a condition where bias voltage of −100V is applied.
In these coated cutting tool, in order to improve their cutting performance, particularly chipping resistance, abrasion resistance, and the like, various sorts of proposals on the structure of the hard coating layer were made.
For example, a coated tool (end mill), in which fracturing resistance is improved by suppressing fracturing of the coating layer on the rake face and abrasion resistance on flank face is further improved, is disclosed in Patent Literature 2 (PTL 2). In the coated tool (end mill) disclosed in PTL 2, the coating layer is constituted by columnar crystals: the coating layer on the rake face is thinner than the coating layer on the flank face: the coating layer is made of two layers, and the average crystal width in the upper layer region on the surface side of the coating layer is larger than that of the lower layer region on the body side of the coating layer: the ratio of the upper layer region to the coating layer on the rake face is less than that on the flank face: the average columnar crystal width on the rake face is less than that on the flank face.
Also, for example, a coated tool, in which abrasion resistance and toughness is balanced at a high level, is disclosed in Patent Literature 3 (PTL 3). The coated tool disclosed in PTL 3 has s coating film with excellent adhesiveness to the body. In the coated tool disclosed in PTL 3, the coating film formed on the body includes the first coating film layer: the first film layer includes the micro-structure region and the coarse-structure region: the average crystal size of the composition constituting the micro-structure region is 10-200 nm: the micro-structure region occupies the range corresponding to the thickness of 50% or more of the total thickness of the first coating film layer from the surface side of the first coating film layer: the micro-structure region has the average compressive stress of −4 GPa or more and −2 GPa or less: the first coating film layer has stress distribution in its thickness direction: there are 2 or more maximum values and minimum values in the stress distribution: the closer to the surface side in the thickness direction, the higher the maximum and the minimum values of the compressive stress.